1. Field of the Invention
The present invention relates to a laminated coil component, such as a laminated inductor, and more particularly, to an open magnetic circuit type laminated coil component including a coil conductor that is disposed inside a laminate in which a magnetic layer and a non-magnetic layer or a low magnetic permeability layer are laminated.
2. Description of the Related Art
Laminated coil components including a coil conductor that is disposed in a laminate formed by laminating a plurality of coil conductor patterns and a plurality of magnetic ceramic layers are widely used. Among the laminated coil components, a closed magnetic circuit type laminated coil component has problems in that, when a superposed direct current is gradually increased, an inductance value is substantially constant or gradually decreases until the superposed direct current reaches a certain current value, but, after exceeding the certain current value, magnetic saturation arises which sharply reduces the inductance value.
In order to solve the problems, an open magnetic circuit type laminated coil component is known in which a non-magnetic ceramic layer is inserted in a laminate, in which magnetic material ceramic layers (magnetic layer) are laminated, near the center of a coil as viewed in the lamination direction (see Japanese Unexamined Patent Application Publication No. 2004-311944).
The open magnetic circuit type laminated coil component of Japanese Unexamined Patent Application Publication No. 2004-311944 includes a spiral coil L formed by electrically connecting a plurality of coil conductor patterns 55 is built into a laminate 60 formed by laminating magnetic material ceramic layers as shown in FIG. 9. The laminate 60 has a coil portion 51 which is a region in which the spiral coil L is disposed and outer layer portions 52 and 53 laminated outside the coil portion 51. A non-magnetic ceramic layer 54 is disposed at the approximate center of the coil L in the lamination direction of the laminate 60. Moreover, external electrodes 56 and 57 connected to the spiral coil L are disposed in the laminate 60.
In the laminated coil component as described above, the magnetic flux φ generated by the spiral coil L crosses the non-magnetic ceramic layer 54 which prevents magnetic saturation.
However, the open magnetic circuit type laminated coil component in which the non-magnetic ceramic layer 54 is inserted into the laminate 60 in which the magnetic material ceramic layers (magnetic layer) are laminated as described above is produced through a process of firing a laminate in which a laminated magnetic layer and a non-magnetic layer are laminated. The open magnetic circuit type laminated coil component has problems in that the interface between the layers suffers from cracking, chipping, peeling, and other defects, and thus, the properties deteriorate due to different shrinkage behaviors, such as a shrinkage starting temperature or a shrinkage rate, of the layers in a process of firing the magnetic layer (magnetic ceramic layer) and the non-magnetic layer (non-magnetic ceramic layer).
For example, in a firing process after the magnetic layer on which the coil conductor pattern 55 is printed and the non-magnetic layer 54 are laminated in a desired order, the non-magnetic layer is usually sintered and shrunk earlier than the magnetic layer. Therefore, there is a problem in that cracking, chipping, peeling, and other defects, are likely to occur at the interface (particularly at the side of the magnetic layer) between the non-magnetic layer 54 and the magnetic layer that is sintered later than the non-magnetic layer.
Moreover, a laminated chip component has been proposed in which magnetic layers are laminated and whose mechanical strength is increased by blending a zirconium oxide in a proportion of 0.01 wt % to 1.2 wt % in Ni—Cu—Zn ferrite which is a magnetic material (see Japanese Unexamined Patent Application Publication No. 7-57922).
However, the laminated chip component has a closed magnetic circuit structure in which only magnetic layers are laminated, is likely to be magnetically saturated, and is limited to attempting to increase direct current superposition characteristics. Therefore, it is problematic for the laminated chip component to be unable to fully satisfy various demands in terms of properties that are particular to the laminated coil component.